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| United States Patent |
5,296,534
|
|
Senuma
, et al.
|
March 22, 1994
|
Flame retardant composition
Abstract
A flame retardant composition comprising:
(i) a thermoplastic resin;
(ii) magnesium hydroxide; and
(iii) an organopolysiloxane modified styrene elastomer.
| Inventors:
|
Senuma; Akitaka (Yokohama, JP);
Yasuda; Nobuo (Yokohama, JP);
Noda; Isao (Yokosuka, JP)
|
| Assignee:
|
Nippon Unicar Company Limited (Tokyo, JP)
|
| Appl. No.:
|
002631 |
| Filed:
|
January 11, 1993 |
Foreign Application Priority Data
| Jan 16, 1992[JP] | 4-25744 |
| Jan 20, 1992[JP] | 4-31601 |
| Current U.S. Class: |
524/436; 525/72; 525/106 |
| Intern'l Class: |
C08K 003/22 |
| Field of Search: |
524/436
525/72,106
|
References Cited
U.S. Patent Documents
| 4067847 | Jan., 1978 | Yui et al. | 260/45.
|
| 4098762 | Jul., 1978 | Miyata et al. | 524/162.
|
| 4535106 | Aug., 1985 | Abolins et al. | 525/106.
|
| 4560719 | Dec., 1985 | Nakamura et al. | 524/436.
|
| 4618654 | Oct., 1986 | Schmidtchen et al. | 525/72.
|
| 4622350 | Nov., 1986 | Icenogle et al. | 523/200.
|
| 4732939 | Mar., 1988 | Hoshi et al. | 524/436.
|
| 4783504 | Nov., 1988 | St. Clair et al. | 525/72.
|
| 4801639 | Jan., 1989 | Hoshi et al. | 524/436.
|
| 4913965 | Apr., 1990 | Keogh | 524/436.
|
| 4921916 | May., 1990 | Howell et al. | 524/436.
|
| 4975486 | Dec., 1990 | Kasahari et al. | 525/75.
|
| 5002996 | Mar., 1991 | Okuda et al. | 524/436.
|
| 5132350 | Jul., 1992 | Keogh | 524/436.
|
| Foreign Patent Documents |
| 61-9401 | Aug., 1981 | JP.
| |
Primary Examiner: Hoke; Veronica P.
Attorney, Agent or Firm: Bresch; Saul R.
Claims
We claim:
1. A composition comprising:
(i) a thermoplastic resin;
(ii) magnesium hydroxide; and
(iii) a styrene elastomer having an organopolysiloxane grafted thereto
wherein for each 100 parts by weight of thermoplastic resin, the other
components are present in about the following amounts:
______________________________________
Component Parts by weight
______________________________________
magnesium hydroxide 5 to 450
organopolysiloxane grafted
1 to 80
styrene elastomer
______________________________________
2. A composition comprising:
(i) a thermoplastic resin;
(ii) magnesium hydroxide;
(iii) an organopolysiloxane;
(iv) a styrene elastomer; and
(v) an organic peroxide
wherein for each 100 parts by weight of thermoplastic resin, the other
components are present in about the following amounts:
______________________________________
Component Parts by weight
______________________________________
magnesium hydroxide
5 to 450
organopolysiloxane
0.1 to 450
styrene elastomer
1 to 450
organic peroxide 0.001 to 5
______________________________________
3. The composition defined in claim 1 wherein the styrene elastomer is a
styrene-ethylene/butylene-styrene triblock copolymer.
4. The composition defined in claim 2 wherein the styrene elastomer is a
styrene-ethylene/butylene-styrene triblock copolymer.
5. A composition comprising:
(i) polyethylene; and, for each 100 parts by weight of polyethylene,
(ii) about 5 to about 450 parts by weight of magnesium hydroxide, surface
treated with a carboxylic acid or a metal salt thereof; and
(iii) about 1 to about 80 parts by weight of a
styrene-ethylene/butylene-styrene triblock copolymer having grafted
thereto a silicone oil or a silicone gum.
6. The composition defined in claim 1 coated on, or extruded about, an
electrical conductor or glass fibers.
7. A molded article comprising the composition defined in claim 1.
Description
TECHNICAL FIELD
This invention relates to flame retardant compositions containing
thermoplastic resins and a magnesium hydroxide filler. The compositions
are particularly useful as insulation for wire and cable.
BACKGROUND ART
Thermoplastic resins, which have good electrical insulation
characteristics, are widely used to provide insulating jacketing or
sheaths for wire and cable. Recently, there has been a demand for improved
flame retardant properties, e.g., as high as V-1 to V-0 using Underwriters
Laboratories standards.
Thermoplastic resin can be made flame retardant by adding to the resin
organic halides or antimony oxides, for example, or the resin itself can
be halogenated to provide polymers such as polyvinyl chloride or
chlorinated polyethylene. These thermoplastic resins, however, on burning,
drip, sag, and emit large amounts of smoke and other harmful gases, and
also corrode metals.
In order to solve these problems, it has been proposed to add metal
hydroxides to non-halogenated thermoplastic resins. Aluminum hydroxide was
first used because of its low cost, but it has such a low decomposition
temperature (170.degree. to 190.degree. C.) that the aluminum hydroxide
decomposes, generating water, which, in turn, causes foaming on interior
surfaces. Furthermore, to obtain a flame retardance of V-1 to V-0,
aluminum hydroxide has to be added to the thermoplastic resin in amounts
of as much as 60 to 65 percent by weight based on the weight of the total
composition.
Compared with aluminum hydroxide, magnesium hydroxide has a much higher
decomposition temperature (about 360.degree. C.), and, thus, exhibits less
foaming. For this reason, and others, magnesium hydroxide has been widely
used as a flame retardant in resins. One disadvantage of a thermoplastic
resin/magnesium hydroxide flame retardant composition, however, is that
the magnesium hydroxide absorbs carbon dioxide from high humidity, high
temperature atmospheres such as the atmosphere found in a cable tunnel.
This results in the formation of magnesium hydroxycarbonate (MgCO.sub.3
.multidot.Mg(OH).sub.2), a white substance, on, for example, the surface
of a wire or cable jacket. This "whitening" not only detracts from the
appearance of the jacket, but also has a degrading effect insofar as arc
resistance, insulation, mechanical, low temperature brittleness, and other
properties are concerned.
Magnesium hydroxide is also not conducive to good moldability. When
combined with a thermoplastic resin, poor flammability, slow molding
speed, rough surfaces, and lower electrical and mechanical properties can
be the result.
DISCLOSURE OF INVENTION
An object of this invention, therefore, is to provide a composition, which,
in a formed state, will not be susceptible to whitening caused by the
chemical reaction of magnesium hydroxide, carbon dioxide, and water, and
will exhibit good moldability and sufficient flame resistance.
Other objects and advantages will become apparent hereafter.
According to the invention, a composition has been discovered which meets
the above objective. The composition comprises
(i) a thermoplastic resin;
(ii) magnesium hydroxide; and
(iii) an organopolysiloxane modified styrene elastomer.
DETAILED DESCRIPTION
The thermoplastic resin can be any homopolymer or copolymer produced from
two or more comonomers, or a blend of two or more of these polymers,
conventionally used as jacketing and/or insulating materials in wire and
cable applications. Generally, the monomers useful in the production of
these homopolymers and copolymers will have 2 to 20 carbon atoms. Examples
of such monomers are alpha-olefins such as ethylene, propylene, 1-butene,
1-hexene, 4-methyl-1-pentene, and 1-octene; unsaturated esters such as
vinyl acetate, ethyl acrylate, methyl acrylate, methyl methacrylate,
t-butyl acrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl
acrylate, and other alkyl acrylates; diolefins such as 1,4-pentadiene,
1,3-hexadiene, 1,5-hexadiene, 1,4-octadiene, and ethylidene norbornene;
other monomers such as styrene, p-methyl styrene, alphamethyl styrene,
vinyl naphthalene, and similar aryl olefins; nitriles such as
acrylonitrile and methacrylonitrile; vinyl methyl ketone, vinyl methyl
ether, and maleic anhydride; and acrylic acid, methacrylic acid, and other
similar unsaturated acids. In addition to polyolefins, included among the
polymers can be polyesters, polycarbonates, and polyurethanes. The
homopolymers and copolymers of ethylene are preferred. The resins are
preferably non-halogenated.
Examples of homopolymers and copolymers of ethylene are high pressure, low
density polyethylene; polyethylenes of various densities (high, medium,
linear low, very low, and ultra-low) wherein the comonomer is 1-butene,
1-hexene, 4-methyl-1-pentene, or 1-octene; ethylene/propylene rubber;
ethylene/propylene/diene monomer rubber; ethylene/vinyl acetate copolymer;
ethylene/ethyl acrylate copolymer; isobutylene/isoprene rubber and
polybutene-1. Preferred densities are in the range of about 0.860 to 0.915
gram per cubic centimeter.
While conventional magnesium hydroxides can be used, a particularly
preferred magnesium hydroxide and a method for its preparation are
described in U.S. Pat. No. 4,098,762. Preferred characteristics for this
magnesium hydroxide are (a) a strain in the <101> direction of no more
than 3.0.times.10.sup.-3 ; (b) a crystallite size in the <101> direction
of more than 800 angstroms; and (c) a surface area, determined by the BET
method, of less than 20 square meters per gram.
The average particle diameter of the magnesium hydroxide can be in the
range of about 0.1 to about 15 microns and is preferably in the range of
about 0.5 to about 3 microns. The surface area can be about 1 to about 20
square meters per gram and is preferably about 3 to about 8 square meters
per gram.
The magnesium hydroxide is preferably surface treated with a saturated or
unsaturated carboxylic acid having about 8 to about 24 carbon atoms and
preferably about 12 to about 18 carbon atoms or a metal salt thereof.
Mixtures of these acids and/or salts can be used, if desired. Examples of
suitable carboxylic acids are oleic, stearic, palmitic, isostearic, and
lauric; of metals which can be used to form the salts of these acids are
zinc, aluminum, sodium, calcium, magnesium, and barium; and of the salts
themselves are magnesium stearate, zinc oleate, sodium oleate, sodium
stearate, sodium lauryl sulfonate, calcium stearate, zinc stearate,
calcium palmitate, magnesium oleate, and aluminum stearate. The amount of
acid or salt can be in the range of about 0.1 to about 5 parts by weight
of acid and/or salt per one hundred parts by weight of metal hydrate and
preferably about 0.25 to about 3 parts by weight per one hundred parts by
weight of metal hydrate. The acid or salt can be merely added to the
composition in like amounts rather than using the surface treatment
procedure, but this is not preferred.
The proportions of components in subject composition based on 100 parts by
weight of thermoplastic resin are about as follows:
______________________________________
Broad Range
Preferred Range
(parts by weight)
______________________________________
Magnesium hydroxide
5 to 450 100 to 250
Organopolysiloxane
1 to 80 30 to 60
modified styrene
elastomer
______________________________________
The weight ratio of magnesium hydroxide to the modified styrene elastomer
can be in the range of about 0.06:1 to about 450:1 and is preferably in
the range of about 1.7:1 to about 8.3:1.
The styrene elastomers include styrene-butadiene rubbers (a copolymer of
styrene and butadiene); styrene-isoprene copolymers;
styrene-isoprene-styrene block copolymers; styrene-butadiene-styrene block
copolymers; alpha-methylstyrene-isoprene-alpha-methylstyrene block
copolymers; styrene-butadiene block copolymers; styrene-isoprene block
copolymers; alpha-methylstyrene-butadiene copolymers;
alpha-methylstyrene-isoprene copolymers;
alpha-methylstyrene-butadiene-alpha-methylstyrene block copolymers; and
styrene-butadiene-isoprene block copolymers. A preferred styrene elastomer
is a styrene-ethylene/butylene-styrene triblock copolymer. All of the
styrene elastomers are thermoplastic rubbers and are based on about 30 to
about 70 percent by weight styrene or alpha-methyl styrene with the
balance being, for example, butadiene, isoprene, or ethylene/butylene
copolymer. The elastomers can be linear, diblock, triblock, or graft
copolymers.
The molecular weight of the styrene elastomer is generally in the range of
about 50,000 to about 200,000 and is preferably in the range of about
80,000 to about 150,000. Other characteristics of the styrene elastomer
are as follows: the density of the elastomer can range from about 0.880 to
about 0.960 gram per cubic centimeter and the melt index from about 1 to
about 10 grams per 10 minutes measured at 230.degree. C. under a 2.16
kilogram load. Flow indices are in the range of about 30 to about 300
grams per 10 minutes measured at 230.degree. C. under a 21.6 kilogram
load.
In the styrene-ethylene/butylene-styrene triblock copolymer, polystyrene
provides the two end blocks and poly(ethylene/butylene) provides the
midblock. The triblock copolymer can be based on about 13 to about 37
percent by weight styrene and about 67 to about 87 percent by weight of a
mixture of ethylene and butylene. The midblock can be saturated or
unsaturated.
The organopolysiloxane used to modify the styrene elastomer can contain
unsaturated or saturated aliphatic groups, and can also contain aromatic
groups. The unsaturated groups can be present in one or more of the
siloxane recurring units, which can be a methyl vinyl siloxane or another
alkyl alkenyl siloxane. These units can be present in the
organopolysiloxane in an amount of at least about 0.5 percent based on the
weight of the organopolysiloxane.
The organopolysiloxane can also have a plasticity in the range of about 30
to about 750 degrees. The term "plasticity" is defined as 100 times the
deformed height in millimeters at 70.degree. C. for 10 minutes. It is
determined under ASTM D-926 (parallel plate).
The unsaturated groups are exemplified by vinyl, allyl, acryl, and
methacryl. The organopolysiloxane can also contain radicals such as
halogen, cyano, and mercapto. The groups or radicals can be the same or
different, and the molecular structure of the organopolysiloxane can be
linear or cyclic and can contain straight or branched chains. A linear
structure is preferred. The number of siloxane units in the
organopolysiloxane can be in the range of about 10 to about 10,000; is
preferably in the range of about 100 to about 1000; and more preferably is
at least about 250. The viscosity of the organopolysiloxane can be at
least about 10 centistokes at 23.degree. C. and is preferably in the range
of about 1000 to about 1,000,000 centistokes at 23.degree. C. Viscosity is
measured by using a Cannon-Fenske.TM. capillary viscometer according to
ASTM D-445-61. When the viscosity is less than about 10 centistokes, there
is a tendency towards exudation on the surface of the resulting foam.
Preferred organopolysiloxanes are silicone gum and silicone oil.
One formula for a suitable organopolysiloxane can be written as follows:
##STR1##
wherein R is hydrogen or an unsubstituted or substituted monovalent
hydrocarbyl radical; each R is the same or different; and n is at least
about 10.
A preferred organopolysiloxane can have the following recurring unit:
##STR2##
wherein R' is a monovalent unsaturated aliphatic group; R" is an
unsubstituted or substituted monovalent saturated aliphatic or aromatic
group; each R" is the same or different; 9<or equal to a<1; 0.5<b<3; and
1<a+b<3. The subscript a is preferably about 0.0004 to about 0.06. The
subscript b is preferably about 1 to about 2. R' can be vinyl or other
alkenyl group having 2 to 10 carbon atoms and R" can be an alkyl such as
methyl, ethyl, or propyl; an aryl such as phenyl or tolyl; or a cycloalkyl
such as cyclohexyl or cyclobutyl. Substituents are exemplified by halogen,
cyano, and mercapto radicals.
An example of a specific recurring unit wherein a+b=2; a=0.1; and b=1.9
follows:
##STR3##
The modification of the styrene elastomer with the organopolysiloxane is
accomplished with an organic peroxide, which preferably has a
decomposition temperature in the range of about 100.degree. to about
220.degree. C. and about a 10 minute half life. Suitable organic peroxides
are as follows (the decomposition temperature in .degree.C. is given in
parentheses):
Succinic acid peroxide (110), benzoyl peroxide (110), t-butyl
peroxy-2-ethylhexanoate (113), p-chlorobenzoyl peroxide (115), t-butyl
peroxyisobutyrate (115), t-butyl peroxyisopropyl carbonate (135), t-butyl
peroxylaurate (140), 2,5-dimethyl-2,5-di(benzoyl peroxy)hexane (140),
t-butyl peroxyacetate (140), di-t-butyl peroxyphthalate (140), t-butyl
peroxymaleate (140) cyclohexanone peroxide (145), t-butyl peroxybenzoate
(145), dicumyl peroxide (150), 2,5-dimethyl-2,5-di(t-butyl peroxy)hexane
(155), t-butyl cumyl peroxy (155), t-butyl hydroperoxide (158), di-t-butyl
peroxide (160), 2,5-dimethyl-2,5-di(t-butyl peroxy)hexene-3 (170),
di-isopropylbenzene hydroperoxide (170), p-methane hydroperoxide (180),
and 2,5-dimethyl hexane-2,5-hydroperoxide (213).
For each 100 parts by weight of thermoplastic resin, the proportions of
organopolysiloxane and organic peroxide are about as follows:
______________________________________
Parts by Weight
Component broad preferred
______________________________________
(ii) organopolysiloxane
0.1 to 450
3 to 20
(iii) organic peroxide
0.001 to 15
0.1 to 2
______________________________________
The components are heat-kneaded together at a temperature of about
160.degree. C. to about 200.degree. C., in kneading apparatus such as a
Banbury.TM. mixer or a twin-screw extruder. The heat-kneading is continued
until the melt index of the combination is in the range of about 0.05 to
about 5 grams per 10 minutes.
The composition adapted to provide the composition of the invention, which
includes a styrene elastomer modified with an organopolysiloxane,
comprises:
(1) a thermoplastic resin;
(ii) magnesium hydroxide;
(iii) an organopolysiloxane;
(iv) a styrene elastomer; and
(v) an organic peroxide
Commercial embodiments of the composition of the invention are generally
obtained by mixing together the above-mentioned components with one or
more antioxidants and other additives in apparatus such as a Banbury
mixer, a pressure kneader, a twin screw extruder, a Buss co-kneader, a
Henschel mixer, or a roll kneader at temperatures in the range of about
160.degree. C. to about 200.degree. C. The result is that the styrene
elastomer is modified by the organopolysiloxane, which grafts thereto. The
components can be added in any order and the components used in smaller
amounts can be added via a masterbatch. The mixtures can then be extruded
or subjected to injection molding, rotational molding, or compression
molding.
Useful additives for the composition of the invention are antioxidants,
surfactants, reinforcing filler or polymer additives, crosslinking agents,
ultraviolet stabilizers, antistatic agents, pigments, dyes, slip agents,
plasticizers, lubricants, viscosity control agents, extender oils, metal
deactivators, water tree growth retardants, voltage stabilizers, flame
retardant additives, and smoke suppressants.
Examples of antioxidants are: hindered phenols such as tetrakis[methylene
(3,5-di-tert-butyl-4-hydroxy-hydrocinnamate)]methane and thiodiethylene
bis(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate; phosphites and
phosphonites such as tris(2,4-di-tert-butylphenyl) phosphite and
di-tert-butylphenylphosphonite; various amines such as polymerized
2,2,4-trimethyl-1,2-dihydroquinoline; and silica. Antioxidants are used in
amounts of about 1 to about 5 parts by weight per hundred parts by weight
of thermoplastic resin.
The patent mentioned in this specification is incorporated by reference
herein.
The invention is illustrated by the following examples.
EXAMPLES
In the examples, the performance of the composition of the invention is
evaluated by using a dumbbell specimen cut out of a sheet formed by
compression molding the composition. The degree of whitening is determined
by measuring the weight increase of a specimen exposed to a carbon dioxide
gas stream containing moisture. The exposure is effected in a glass
chamber having a volume of 50 cubic centimeters. The carbon dioxide is
introduced into the chamber after bubbling through water at room
temperature to provide a gas stream having a relative humidity higher than
90 percent.
Moldability is determined in terms of melt index and melt flow index. The
melt index is measured at 190.degree. C. under a loading of 2.16 kilograms
and the melt flow index is measured at 190.degree. C. under a loading of
21.6 kilograms, both in accordance with JIS (Japanese Industrial Standard)
K-6760. Moldability is considered good when the melt index is 0.1 gram per
10 minutes or greater and the melt flow index is 30 grams per 10 minutes
or greater.
Flame retardance is determined in terms of oxygen index in accordance with
JIS K-7210. Flame retardance is considered sufficient if the oxygen index
is 31 or greater.
EXAMPLE 1
40 parts by weight of silicone gum containing 0.8 percent by weight methyl
vinyl siloxane and having a plasticity of 80 degrees; 100 parts by weight
styrene-ethylene/butylene-styrene triblock copolymer (SEBS); and 0.07 part
by weight 1,3-di(t-butyl peroxy isopropyl)benzene (organic peroxide) are
kneaded at 180.degree. C. for 10 minutes to obtain an organopolysiloxane
modified styrene elastomer. 100 parts by weight of a high pressure low
density polyethylene; 200 parts by weight of magnesium hydroxide coated
with stearic acid; 0.5 part by weight of an antioxidant; 2.5 parts by
weight of carbon black; and 15 parts by weight of the organopolysiloxane
modified styrene elastomer prepared above are kneaded at 170.degree. C.
for 10 minutes in a Banbury.TM. mixer.
The antioxident is tetrakis[methylene
(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]methane.
The resulting kneaded mixture has a melt index of 0.12 g/10 min and a melt
flow index of 38 g/10 min and has good moldability.
The kneaded mixture is pelletized, and the pellets are formed into a sheet,
one millimeter thick, 150 millimeters in length, and 180 millimeters in
width at 150.degree. C. and 100 kilograms per square centimeter for 3
minutes. A dumbbell sample is provided out of the sheet for the whitening
test described above.
The sample takes 19 days to increase its weight by one percent; the longer
the period of time the better. The results of the accelerated test suggest
that it will take 3500 days (over nine years) for the sample to incur the
same weight increase when exposed to a normal atmosphere containing 0.03
percent by weight carbon dioxide. Thus, it can be said that the subject
composition has sufficient resistance to whitening caused by carbon
dioxide gas for commercial applications.
In a visual test, it took 10 days before a white substance appeared on the
surface of the sample, and 23 days before the surface of the sample was
completely white. These periods in the accelerated test translate into 800
days and 3800 days, respectively, in a normal atmosphere containing 0.3
percent by weight carbon dioxide.
The oxygen index is 34. Thus, the sample has sufficient flame retardance.
EXAMPLE 2
Example 1 is repeated except that 30 parts by weight of the modified
styrene elastomer are used.
The resulting kneaded mixture has a melt index of 0.18 g/10 min and a melt
flow index of 48 g/10 min and has good moldability.
The sample takes 17 days to increase its weight by one percent.
The oxygen index is 35.
EXAMPLE 3
Example 2 is repeated except that a linear very low density polyethylene is
used instead of the high pressure low density polyethylene.
The resulting kneaded mixture has a melt index of 0.13 g/10 min and a melt
flow index of 29 g/10 min, and has good moldability.
The sample takes 15 days to increase its weight by one percent.
The oxygen index is 35.
EXAMPLE 4
This is a comparative example.
Example 1 is repeated except that the modified styrene elastomer is
omitted.
The resulting kneaded mixture has a melt index of 0.08 g/10 min and a melt
flow index of 17 g/10 min, and poor moldability.
The sample takes 6 days to increase its weight by one percent.
The oxygen index is 33.
EXAMPLE 5
This is a comparative example.
Example 3 is repeated except that the modified styrene elastomer is
omitted. The resulting kneaded mixture has a melt index of 0.09 g/10 min
and a melt flow index of 13, and has poor moldability.
The sample takes 9 days to increase its weight by one percent.
The oxygen index is 33.
EXAMPLE 6
Example 1 is repeated except that the modified styrene elastomer is not
prepared initially.
Instead, it is prepared in the second kneading step. To the polyethylene,
coated magnesium hydroxide, antioxidant, and carbon black are added 11
parts by weight SEBS; 5 parts by weight of the silicone gum; and 0.15
parts by weight of the organic peroxide, and the second kneading step is
effected.
The resulting kneaded mixture has a melt index of 0.16 g/10 min. and a melt
flow index of 37 g/10 min, and has good moldability.
The whitening results and the oxygen index are the same as in Example 1.
EXAMPLE 7
Example 6 is repeated except that 100 parts by weight of the coated
magnesium hydroxide; 22 parts by weight of SEBS; and 10 parts by weight of
silicone gum are used.
The resulting kneaded mixture has a melt index of 0.23 g/10 min and a melt
flow index of 47 g/10 min, and has good moldability.
The sample takes 18 days to increase its weight by one percent. In a visual
test, it takes 9 days before a white substance appears on the surface of
the sample and 22 days before the surface of the sample is completely
white.
The oxygen index is 35.
EXAMPLE 8
Example 6 is repeated except that a low pressure low density polyethylene
is substituted for the high pressure low density polyethylene.
The resulting kneaded mixture has a melt index of 0.16 g/10 min and a melt
flow index of 30 g/10 min.
The sample takes 16 days to increase its weight by one percent. In a visual
test, it takes 8 days before a white substance appears on the surface of
the sample and 18 days before the surface of the sample is completely
white.
The oxygen index is 34.
EXAMPLE 9
This is a comparative example.
Example 6 is repeated except that the SEBS, the silicone gum, and the
organic peroxide are omitted.
The resulting kneaded mixture has a melt index of 0.08 g/10 min and a melt
flow index of 17 g/10 min, and has poor moldability.
The oxygen index is 33.
EXAMPLE 10
This is a comparative example.
Example 6 is repeated except that 16 parts by weight of SEBS is used, and
the silicone gum and organic peroxide are omitted.
The resulting kneaded mixture has a melt index of 0.16 g/10 min and a melt
flow index of 37 g/min, and has good moldability.
The oxygen index is 30, and the sample shows insufficient flame retardance.
EXAMPLE 11
This is a comparative example.
Example 8 is repeated except that the SEBS, silicone gum, and the organic
peroxide are omitted.
The resulting kneaded mixture has a melt index of 0.09 g/10 min and a melt
flow index of 13 g/10 min, and has poor moldability.
The oxygen index is 33.
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